Sympathetic nervous system responses typically are regionally differentiated, with activation in one outflow sometimes accompanying no change or sympathetic inhibition in another. Regional ...sympathetic activity is best studied in humans by recording from postganglionic sympathetic efferents (multiunit or single fiber recording) and by isotope dilution-derived measurement of organ-specific norepinephrine release to plasma (regional "norepinephrine spillover"). Evidence assembled in this review indicates that sympathetic nervous system abnormalities are crucial in the development of cardiovascular disorders, notably heart failure, essential hypertension, disorders of postural circulatory control causing syncope, and "psychogenic heart disease," heart disease attributable to mental stress and psychiatric illness. These abnormalities involve persistent, adverse activation of sympathetic outflows to the heart and kidneys in heart failure and hypertension, episodic or ongoing cardiac sympathetic activation in psychogenic heart disease, and defective sympathetic circulatory reflexes in disorders of postural circulatory control. An important goal for clinical scientists is translation of knowledge of pathophysiology, such as this, into better treatment for patients. The achievement of this "mechanisms-to-management" transition is at differing stages of development with the different conditions. Clinical translation is mature in cardiac failure, knowledge of cardiac neural pathophysiology having led to introduction of beta-adrenergic blockers, an effective therapy. With essential hypertension, perhaps we are on the cusp of effective translation, with recent successful testing of selective catheter-based renal sympathetic nerve ablation in patients with resistant hypertension, an intervention firmly based on demonstration of activation of the renal sympathetic outflow. With psychogenic heart disease and postural syncope syndromes, knowledge of the neural pathophysiology is emerging, but clinical translation remains for the future.
The seventeenth century London neuroanatomical school headed by Thomas Willis published the first images of the sympathetic nervous system. Nineteenth century European physiologists characterised ...these as the “pressor nerves”. Von Euler’s demonstration that the sympathetic transmitter was norepinephrine brought the field into the modern era. Sympathetic nervous system responses are regionally differentiated; human regional sympathetic activity is best studied by recording from postganglionic sympathetic efferents directed to the skeletal muscle vasculature (clinical microneurography) and by measurement of organ-specific norepinephrine release to plasma from sympathetic nerves (regional “norepinephrine spillover”). With these techniques, the sympathetic nervous system became accessible to clinical scientists, allowing the demonstration that sympathetic nervous system activation is crucial in the development and outcomes of cardiovascular disorders, most notably heart failure and essential hypertension. Activation of the renal sympathetic outflow is pivotal in the pathogenesis of essential hypertension. An important goal for clinical scientists is translation of knowledge of pathophysiology, such as this, into better treatment for patients. Although disputed, the case is strong that in hypertension, we are now on the cusp of effective “mechanisms to management” transition, with the use of catheter-based renal sympathetic nerve ablation for treating drug-resistant hypertension.
Several articles have dealt with the importance and mechanisms of the sympathetic nervous system alterations in experimental animal models of hypertension. This review addresses the role of the ...sympathetic nervous system in the pathophysiology and therapy of human hypertension. We first discuss the strengths and limitations of various techniques for assessing the sympathetic nervous system in humans, with a focus on heart rate, plasma norepinephrine, microneurographic recording of sympathetic nerve traffic, and measurements of radiolabeled norepinephrine spillover. We then examine the evidence supporting the importance of neuroadrenergic factors as promoters and amplifiers of human hypertension. We expand on the role of the sympathetic nervous system in 2 increasingly common forms of secondary hypertension, namely hypertension associated with obesity and with renal disease. With this background, we examine interventions of sympathetic deactivation as a mode of antihypertensive treatment. Particular emphasis is given to the background and results of recent therapeutic approaches based on carotid baroreceptor stimulation and radiofrequency ablation of the renal nerves.
The Achilles heel in catheter-based studies of renal denervation for severe hypertension is the almost universal failure to apply a confirmatory test for renal denervation. When renal denervation ...efficacy was assessed, using measurements of the spillover of norepinephrine from the renal sympathetic nerves to plasma, the only test validated to this point, denervation was found to be incomplete and nonuniform between patients. It is probable that the degree of denervation has typically been suboptimal in renal denervation trials. This criticism applies with special force to the Symplicity HTN-3 trial, where the proceduralists, although expert interventional cardiologists, had no prior experience with the renal denervation technique. Their learning curve fell during the trial, a shortcoming accentuated by the fact that one-third of operators performed one procedure only. Recently presented results from the Symplicity HTN-3 trialists confirm that renal denervation was not effectively or consistently achieved in the trial.
Summary Background Renal denervation (RDN) with radiofrequency ablation substantially reduces blood pressure in patients with treatment-resistant hypertension. We assessed the long-term ...antihypertensive effects and safety. Methods Symplicity HTN-1 is an open-label study that enrolled 153 patients, of whom 111 consented to follow-up for 36 months. Eligible patients had a systolic blood pressure of at least 160 mm Hg and were taking at least three antihypertensive drugs, including a diuretic, at the optimum doses. Changes in office systolic blood pressure and safety were assessed every 6 months and reported every 12 months. This study is registered with ClinicalTrials.gov , numbers NCT00483808 , NCT00664638 , and NCT00753285. Findings 88 patients had complete data at 36 months. At baseline the mean age was 57 (SD 11) years, 37 (42%) patients were women, 25 (28%) had type 2 diabetes mellitus, the mean estimated glomerular filtration rate was 85 (SD 19) mL/min per 1·73 m2 , and mean blood pressure was 175/98 (SD 16/14) mm Hg. At 36 months significant changes were seen in systolic (−32·0 mm Hg, 95% CI −35·7 to −28·2) and diastolic blood pressure (−14·4 mm Hg, −16·9 to −11·9). Drops of 10 mm Hg or more in systolic blood pressure were seen in 69% of patients at 1 month, 81% at 6 months, 85% at 12 months, 83% at 24 months, and 93% at 36 months. One new renal artery stenosis requiring stenting and three deaths unrelated to RDN occurred during follow-up. Interpretation Changes in blood pressure after RDN persist long term in patients with treatment-resistant hypertension, with good safety. Funding Ardian LLC/Medtronic Inc.
Translational medicine is concerned with the translation of research discoveries into clinical applications for the prevention, diagnosis, and treatment of human diseases. Here we briefly review the ...research concerning the role of the renal sympathetic nerves (efferent and afferent) in the control of renal function, with particular reference to hypertension. The accumulated evidence is compelling for a primary role of the renal innervation in the pathogenesis of hypertension. These research discoveries led to the development of a catheter-based procedure for renal denervation in human subjects. A proof-of-principle study in patients with hypertension resistant to conventional therapy has demonstrated that the procedure is safe and produces renal denervation with sustained lowering of arterial pressure.
Renal sympathetic nerve activation contributes to the pathogenesis of hypertension. Symplicity HTN-2, a multicenter, randomized trial, demonstrated that catheter-based renal denervation produced ...significant blood pressure lowering in treatment-resistant patients at 6 months after the procedure compared with control, medication-only patients. Longer-term follow-up, including 6-month crossover results, is now presented.
Eligible patients were on ≥3 antihypertensive drugs and had a baseline systolic blood pressure ≥160 mm Hg (≥150 mm Hg for type 2 diabetics). After the 6-month primary end point was met, renal denervation in control patients was permitted. One-year results on patients randomized to immediate renal denervation (n=47) and 6-month postprocedure results for crossover patients are presented. At 12 months after the procedure, the mean fall in office systolic blood pressure in the initial renal denervation group (-28.1 mm Hg; 95% confidence interval, -35.4 to -20.7; P<0.001) was similar to the 6-month fall (-31.7 mm Hg; 95% confidence interval, -38.3 to -25.0; P=0.16 versus 6-month change). The mean systolic blood pressure of the crossover group 6 months after the procedure was significantly lowered (from 190.0±19.6 to 166.3±24.7 mm Hg; change, -23.7±27.5; P<0.001). In the crossover group, there was 1 renal artery dissection during guide catheter insertion, before denervation, corrected by renal artery stenting, and 1 hypotensive episode, which resolved with medication adjustment.
Control patients who crossed over to renal denervation with the Symplicity system had a significant drop in blood pressure similar to that observed in patients receiving immediate denervation. Renal denervation provides safe and sustained reduction of blood pressure to 1 year.
Abstract At the seven-year anniversary of the first catheter-based renal denervation procedure for resistant hypertension, it is timely to reflect on the past, present, and future of the development ...and clinical application of this treatment. Unresolved procedural and technical questions are central: How much renal denervation is optimal? How can this level of denervation be achieved? What test for denervation can be applied in renal denervation trials? Will renal denervation show a “class effect,” with the different energy forms now used for renal nerve ablation producing equivalent blood pressure lowering? When I have assessed renal denervation efficacy, using measurements of the spillover of norepinephrine from the renal sympathetic nerves to plasma, the only test validated to this point, denervation was found to be incomplete and non-uniform between patients. It is probable that the degree of denervation has commonly been suboptimal in renal denervation trials; this criticism applying with special force to the Symplicity HTN-3 trial, where the proceduralists, although expert interventional cardiologists, had no prior experience with the renal denervation technique. Recently presented results from the Symplicity HTN-3 trial confirm that renal denervation was not achieved effectively or consistently. Given this, and other difficulties in the execution of the trial relating to drug adherence, an idea mooted is that the US pivotal trial of the future may be in younger, untreated patients.
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